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Mammal stuff: middle ear evolution and mammoth extinction

From: Ben Creisler

OK--not dino or strictly Mesozoic, but may be of interest:

Neal Anthwal, Leena Joshi and Abigail S. Tucker (2012)
Evolution of the mammalian middle ear and jaw: adaptations and novel structures.
Journal of Anatomy (advance online publication)
doi: 10.1111/j.1469-7580.2012.01526.x

Having three ossicles in the middle ear is one of the defining
features of mammals. All reptiles and birds have only one middle ear
ossicle, the stapes or columella. How these two additional ossicles
came to reside and function in the middle ear of mammals has been
studied for the last 200 years and represents one of the classic
example of how structures can change during evolution to function in
new and novel ways. From fossil data, comparative anatomy and
developmental biology it is now clear that the two new bones in the
mammalian middle ear, the malleus and incus, are homologous to the
quadrate and articular, which form the articulation for the upper and
lower jaws in non-mammalian jawed vertebrates. The incorporation of
the primary jaw joint into the mammalian middle ear was only possible
due to the evolution of a new way to articulate the upper and lower
jaws, with the formation of the dentary-squamosal joint, or TMJ in
humans. The evolution of the three-ossicle ear in mammals is thus
intricately connected with the evolution of a novel jaw joint, the two
structures evolving together to create the distinctive mammalian


G.M. MacDonald, D.W. Beilman, Y.V. Kuzmin, L.A. Orlova, K.V.
Kremenetski, B. Shapiro,
R.K. Wayne & B. Van Valkenburgh (2012)
Pattern of extinction of the woolly mammoth in Beringia.
Nature Communications (3): article 893

Extinction of the woolly mammoth in Beringia has long been subject to
research and speculation. Here we use a new geo-referenced database of
radiocarbon-dated evidence to show that mammoths were abundant in the
open-habitat of Marine Isotope Stage 3 (~45–30 ka). During the Last
Glacial Maximum (~25–20 ka), northern populations declined while those
in interior Siberia increased. Northern mammoths increased after the
glacial maximum, but declined at and after the Younger Dryas
(~12.9–11.5 ka). Remaining continental mammoths, now concentrated in
the north, disappeared in the early Holocene with development of
extensive peatlands, wet tundra, birch shrubland and coniferous
forest. Long sympatry in Siberia suggests that humans may be best seen
as a synergistic cofactor in that extirpation. The extinction of
island populations occurred at ~4 ka. Mammoth extinction was not due
to a single cause, but followed a long trajectory in concert with
changes in climate, habitat and human presence.

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